27 August 2004
27 August 2004
With hundreds of thousands of the nation’s bridges nearing the end of their design lives, cash-strapped states are searching for innovative solutions to repair and replace their decaying structures.
One answer may lie in the same material that delivered the stealth aircraft, according to two researchers at the University of Missouri-Rolla.
Composite fibre-reinforced polymer (FRP), first developed for use in the aerospace and automotive industries, may be able to help nurse the rapidly aging national highway infrastructure beyond its intended lifespan.
Dr. Antonio Nanni, the Vernon and Maralee Jones Distinguished Professor of Civil Engineering at UMR, and Dr. John Myers, assistant professor of civil engineering at UMR, are researching how the composite materials can be used to rehabilitate existing structures as well as to construct new bridges.
The researchers are treating five decaying bridges in rural Missouri with a corrosion-resistant bandage of sorts made of this material. Like a bandage, the composite material is lightweight and flexible. Strips of the material can be wrapped around pillars or wallpapered on lengths of concrete to strengthen the original structure. These composite materials combine the strength of aramid, carbon and glass fibres with the stability of the polymer resins.
“In the repair and rehabilitation of building and civil infrastructure, these FRP materials may be very competitive on a first-cost basis,” Nanni says. “Composites are also more durable than steel, as well as lightweight.”
Not only can the high-performance material be wrapped around beams or other structures to provide additional support, but it also can be fashioned into reinforcement bars and inserted into concrete structures or soil before being covered with a sheet of polymer to strengthen the bridge bed. “This technology is ideal for strengthening and repair, and almost unmatchable for seismic upgrade,” Nanni says. “Yet the greatest opportunity is in the replacement of conventional materials for new construction.”
In 2000, the first fully composite bridge in Missouri was installed on the UMR campus. “At UMR, we demonstrated that a bridge can be built with off-the-shelf FRP tubes readily available from the pultrusion (or composite material) industry,” Nanni adds. “We also demonstrated that FRP is an ideal material system to integrate health monitoring features.”
The need for a cost-effective solution to deficient bridges hits close to home for the researchers, as 28 percent of Missouri’s bridges were found to be in poor condition according to a 2003 study by the Federal Highway Administration. De-icing salts and other materials cause significant corrosion decay on steel-reinforced concrete bridges, quickly aging the structures. Bridges that are structurally deficient are often posted for lower weight or are closed if they are found to be unsafe.
The researchers are employing four different FRP technologies as well as steel-reinforced polymer in the bridges, and will test the structures over a number of years to determine whether the composite materials can provide a long-term solution. “We are interested in monitoring durability as it pertains to both the FRP and the concrete substrate,” Nanni says. “In one bridge, we have not repaired the concrete and wish to determine how rapidly the deterioration process would continue on the existing materials, the concrete and its steel reinforcement.”
Nanni leads the Center for Infrastructure Engineering Studies (CIES) at UMR. Myers is one of the center’s research investigators. Other UMR researchers working with Nanni and Myers on the bridge research include Grzegorz Galecki, associate research professor of rock mechanics and explosives; Norbert Maerz, assistant professor of geological and petroleum engineering; Steve Watkins, associate professor of electrical and computer engineering; and Reza Zoughi, the Schlumberger Professor of Electrical and Computer Engineering.
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